[PATCH] D21165: Disable MSan-hostile loop unswitching.

[Evgeniy Stepanov via llvm-commits]

eugenis updated this revision to Diff 60382.

Repository:
  rL LLVM

http://reviews.llvm.org/D21165

Files:
  lib/Transforms/Scalar/LoopUnswitch.cpp

Index: lib/Transforms/Scalar/LoopUnswitch.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnswitch.cpp
+++ lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -188,6 +188,8 @@
     BasicBlock *loopHeader;
     BasicBlock *loopPreheader;
 
+    LoopSafetyInfo SafetyInfo;
+
     // LoopBlocks contains all of the basic blocks of the loop, including the
     // preheader of the loop, the body of the loop, and the exit blocks of the
     // loop, in that order.
@@ -431,6 +433,9 @@
   currentLoop = L;
   Function *F = currentLoop->getHeader()->getParent();
 
+  if (F->hasFnAttribute(Attribute::SanitizeMemory))
+    computeLoopSafetyInfo(&SafetyInfo, L);
+
   EnabledPGO = F->getEntryCount().hasValue();
 
   if (LoopUnswitchWithBlockFrequency && EnabledPGO) {
@@ -524,12 +529,26 @@
       return false;
   }
 
+  bool SanitizingMemory = currentLoop->getHeader()->getParent()->hasFnAttribute(
+      Attribute::SanitizeMemory);
+
   // Loop over all of the basic blocks in the loop.  If we find an interior
   // block that is branching on a loop-invariant condition, we can unswitch this
   // loop.
   for (Loop::block_iterator I = currentLoop->block_begin(),
          E = currentLoop->block_end(); I != E; ++I) {
     TerminatorInst *TI = (*I)->getTerminator();
+
+    // Unswitching on a potentially uninitialized predicate is not
+    // MSan-friendly. Limit this to the cases when the original predicate is
+    // guaranteed to execute, to avoid creating a use-of-uninitialized-value
+    // in the code that did not have one.
+    // This is a workaround for the discrepancy between LLVM IR and MSan
+    // semantics. See PR28054 for more details.
+    if (SanitizingMemory &&
+        !isGuaranteedToExecute(*TI, DT, currentLoop, &SafetyInfo))
+      continue;
+
     if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
       // If this isn't branching on an invariant condition, we can't unswitch
       // it.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D21165.60382.patch
Type: text/x-patch
Size: 1966 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160610/03c6258d/attachment.bin>